An objective lens for recording and/or reproducing information of an optical information recording medium, comprises a first lens group having a positive refractive power and a second lens group having a positive refractive power. The first lens group and the second lens group are arranged in this order from a light source side. The objective lens is a finite conjugate type to converge a divergent light flux from a light source onto an information recording plane of the optical information recording medium and satisfies the following formula:NA≧0.65where NA is an image-side numerical aperture necessary for conducting recording and/or reproducing information of the optical information recording medium.
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3. The objective lens of claim 1 , wherein the objective lens is made of an optical material having an internal transmittance of 85% or more in the thickness of 3 mm in a used wavelength region of 600 nm or less.
6. The objective lens of claim 5 , wherein the objective lens is made of an optical material having an internal transmittance of 85% or more in the thickness of 3 mm in a used wavelength region of 600 nm or less.
9. The objective lens of claim 8 , wherein the objective lens is made of an optical material having an internal transmittance of 85% or more in a thickness of 3 mm in a used wavelength region of 600 nm or less.
11. The objective lens of claim 10 , wherein when the light source generates a wavelength fluctuation within ±10 nm, the diffractive structure has a function to suppress a longitudinal chromatic aberration caused by a refractive index dispersion of an optical material of the objective lens due to the wavelength fluctuation of the light source.
13. The objective lens of claim 10 , wherein the first lens group has a meniscus shape in which a convex surface faces toward the light source side and comprises a ring-shaped diffractive structure on a lens surface placed closest to the optical information recording medium side in the first lens group, and the following formula is satisfied: 0.05 ≦PD/PT≦ 0.25 where PD is a power (mm −1 ) of only a diffractive structure defined by the formula of PD=Σ(−2·b 2i ) when the diffractive structure formed on i th surface is represented by an optical path difference function defined by the formula of Φb=b 2i h 2 +b 4i h 4 +b 6i h 6 + . . . (here, h is a height (mm) from an optical axis and b 2i , b 4i , b 6i , . . . are 2nd order, 4 th order, 6 th order, optical path difference function coefficients respectively), and PT is a power (mm −1 ) of the total system of the objective lens including a power as a refractive lens and a power of the diffractive structure.
15. The objective lens of claim 10 , wherein the following formula is satisfied: 0.2≦/( Ph/Pf −2/≦3.0 where Pf is a distance (mm) between adjoining ring-shaped diffractive zones at an image-side numerical aperture necessary for conducting recording and/or reproducing for an optical information recording medium, and Ph is a distance (mm) between adjoining ring-shaped diffractive zones at a numerical aperture half of the image-side numerical aperture necessary for conducting recording and/or reproducing for an optical information recording medium.
17. The objective lens of claim 10 , wherein an amount of a ni th ordered diffracted light ray generated by the diffractive structure formed at the i th surface is largest among any other ordered diffracted light rays and the objective lens converges the ni th ordered diffracted light ray generated by the diffractive structure onto an information recording plane of the optical information recording medium, where n is an integer other than 0 and ±1.
19. The converging optical system of claim 18 , further comprising a correcting structure provided between the light source and the information recording plane and to correct a spherical aberration generated in the converging optical system.
20. The converging optical system of claim 19 , wherein the correcting structure comprises at least one optical element displaceable along the optical axis so as to change a degree of divergence of the outgoing light flux.
21. The converging optical system of claim 20 , wherein the optical element displaceable along the optical axis is one of the first and second lens groups of the objective lens.
22. The converging optical system of claim 21 , wherein the optical element displaceable along the optical axis is provided between the light source and the objective lens.
23. The converging optical system of claim 20 , wherein the optical element displaceable along the optical axis is made of an optical plastic material.
24. The converging optical system of claim 19 , wherein the correcting structure is an element provided between the light source and the information recording plane and operable for changing a refractive index distribution in the direction perpendicular to the optical axis.
25. The converging optical system of claim 19 , wherein the correcting structure is an element provided between the objective lens and the optical information recording medium and operable for changing a refractive index.
26. The converging optical system of claim 18 , wherein the converging optical system conducts recording and/or reproducing information of an information recording medium which has a plurality of information recording layers on the same light flux incident side, and the correcting structure corrects a fluctuation of a spherical aberration caused by differences in thickness of transparent base boards from the light flux incident surface to respective information recording layers at the time of focus jump among the plurality of information recording layers.
28. An optical pickup apparatus for recording and/or reproducing information comprising: a light source; and a converging optical system having the converging optical system described in claim 18 .
29. A voice and/or image recording and/or voice and/or image reproducing apparatus with recording or reproducing information of an optical recording medium having the optical pickup apparatus of claim 28 .
30. The voice and/or image recording and/or voice and/or image reproducing apparatus of claim 29 , wherein the finite conjugate type objective lens is made of an optical material having an internal transmittance of 85% or more in the thickness of 3 mm in a used wavelength region of 600 nm or less.
31. The optical pickup apparatus of claim 28 , wherein the finite conjugate type objective lens is made of an optical material having an internal transmittance of 85% or more in the thickness of 3 mm in a used wavelength region of 600 nm or less.
33. The converging optical system of claim 32 , wherein when the light source generates a wavelength fluctuation within ±10 nm, the diffractive structure has a function to suppress a longitudinal chromatic aberration caused by a refractive index dispersion of an optical material of the optical element due to the wavelength fluctuation of the light source.
35. The converging optical system of claim 32 , wherein an amount of a n th ordered diffracted light ray generated by the diffractive structure is largest among any other ordered diffracted light rays and the converging optical system converges the n th ordered diffracted light ray generated by the diffractive structure onto an information recording plane of the optical information recording medium, where n is an integer other than 0 and ±1.
37. The converging optical system of claim 36 , wherein the correcting structure comprises at least one optical element displaceable along the optical axis so as to change a degree of divergence of the outgoing light flux.
38. The converging optical system of claim 37 , wherein the optical element displaceable along the optical axis is one of the first and second lens groups of the objective lens.
39. The converging optical system of claim 38 , wherein the optical element displaceable along the optical axis is provided between the light source and the objective lens.
40. The converging optical system of claim 37 , wherein the optical element displaceable along the optical axis is made of an optical plastic material.
41. The converging optical system of claim 36 , wherein the correcting structure is an element provided between the light source and the information recording plane and capable of changing a refractive index distribution in the direction perpendicular to the optical axis.
42. The converging optical system of claim 36 , wherein the correcting structure is an element provided between the objective lens and the optical information recording medium and capable of changing a refractive index.
45. The objective lens of any one of claims 1 , 5 , 8 and 10 , wherein the objective lens comprise at least two aspherical surfaces among surfaces located between a surface of the first lens group positioned closest to the light source and a surface of the second lens group positioned closest to the light source.
50. The objective lens of any one of claims 1 , 5 , 8 and 10 , wherein the objective lens comprises a lens group made of an optical plastic material.
51. The objective lens of any one of claims 1 , 5 , 8 and 10 , wherein the objective lens comprises a lens group made of an optical glass material.
52. The objective lens of any one of claims 1 , 5 , 8 and 10 , wherein the objective lens comprises a diaphragm to regulate the light flux and the diaphragm is provided between a plane that is perpendicular to the optical axis and is tangent to the vertex of the surface of the i th lens group closest to the light source and a surface of the i th lens group closest to the light source.
53. The objective lens of any one of claims 1 , 5 , 8 and 10 , wherein the objective lens regulates a converged light flux diameter by providing a section changing discontinuously in a vertical direction of the surface on at least one surface at a position corresponding to an image-side numerical aperture necessary for conducting recording and/or reproducing information of an optical information recording medium.
55. A converging optical system for recording and/or reproducing information of an optical information recording medium, comprising: an optical element including a finite conjugate type objective lens to converge a divergent light flux having a wavelength of 600 nm or less from a light source onto an information recording plane of the optical information recording medium; the objective lens comprising a first lens group having a positive refractive power and a second lens group having a positive refractive power; wherein the first lens group and the second lens group are arranged in this order from a light source side, and a ring-shaped diffractive structure provided at least one surface of the optical element; and wherein the converging optical system comprises the objective lens described in any one of claims 1 , 5 , 8 and 10 .
56. An optical pickup apparatus for recording and/or reproducing information of an optical information recording medium, comprising: a light source; a converging optical system having a finite conjugate type objective lens to converge a divergent light flux from the light source onto an information recording plane of the optical information recording medium; the objective lens comprising a first lens group having a positive refractive power and a second lens group having a positive refractive power; wherein the first lens group and the second lens group are arranged in this order from a light source side, the light source structured to be displaceable along the direction of the optical axis so as to change the degree of divergence of the light flux going to be incident to the objective lens; a detector to detect a fluctuation of a spherical aberration generated in the converging optical axis; and a driver to displace the light source along the direction of the optical axis so as to reduce the fluctuation of the spherical aberration in accordance with a detection result of the detector; and wherein the optical pickup apparatus comprises the objective lens described in any one of claims 1 , 5 , 8 and 10 .
57. A voice and/or image recording and/or voice and/or image reproducing apparatus, comprising: an optical pickup apparatus for recording and/or reproducing information of an optical information recording medium, which comprises: a light source; a converging optical system having a finite conjugate type objective lens to converge a divergent light flux from the light source onto an information recording plane of the optical information recording medium; the objective lens comprising a first lens group having a positive refractive power and a second lens group having a positive refractive power; wherein the first lens group and the second lens group are arranged in this order from a light source side, the light source structured to be displaceable along the direction of the optical axis so as to change the degree of divergence of the light flux going to be incident to the objective lens; a detector to detect a fluctuation of a spherical aberration generated in the converging optical axis; and a driver to displace the light source along the direction of the optical axis so as to reduce the fluctuation of the spherical aberration in accordance with a detection result of the detector; and wherein the optical pickup apparatus comprises the objective lens described in any one of claims 1 , 5 , 8 and 10 .
62. The converging optical system of any one of claims 36 to 42 , wherein the converging optical system conducts recording and/or reproducing information of an information recording medium which has a plurality of information recording layers on the same light flux incident side, and the correcting structure corrects a fluctuation of a spherical aberration caused by differences in thickness of transparent base boards from the light flux incident surface to respective information recording layers at the time of focus jump among the plurality of information recording layers.
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April 15, 2002
August 9, 2005
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